class Regexp

Regexp.json_create(x) # => /foo/

\Method +JSON.create+ deserializes such a hash, returning a \Regexp object:

# => {"json_class"=>"Regexp", "o"=>0, "s"=>"foo"}
x = /foo/.as_json
require 'json/add/regexp'

returning a 2-element hash representing +self+:
\Method Regexp#as_json serializes +self+,

see Marshal[https://docs.ruby-lang.org/en/master/Marshal.html].
to serialize and deserialize a \Regexp object;
Methods Regexp#as_json and +Regexp.json_create+ may be used

def as_json(*)
  {
    JSON.create_id => self.class.name,
    'o'            => options,
    's'            => source,
  }
end